isGeneratePrecedingState

Determine whether or not the state preceding the invokation of the Command
should also be generated if a historied Node is found to be dirty.

Generally speaking, implementations should not have to exercise any
conditions; Either a preceding state should always be generated (e.g.
a refactoring Command), or never generated (e.g. a Save command). The
result of this method will only be considered if a historied Node
was first found to be dirty before the invokation of the Command.

Commands of type MULTI_DOCUMENT are always treated as
HistoryGeneratingCommands and thus need not implement this interface.